This invention relates to linear position transducers of the type comprising a linear magnetostrictive wire into which a signal is induced by applying a torsional strain along the wire and by action of a piezo electric actuator in contact with the wire. In particular, the invention relates to an improved housing for holding the piezo electric actuator in mechanical contact with the wire.
It is well know to utilize magnetostrictivity in linear distance or position measuring devices, see, for instance, U.S. Pat. No. Krisst 4,071,818; Chamuel U.S. Pat. No. 4,144,559; Ueda, et al U.S. Pat. No. 4,238,844; Bailey, et al U.S. Pat. No. 3,423,673; Tellerman U.S. Pat. No. 3,898,555 and Koski, et al U.S. Pat. No. 4,839,590; all incorporated by reference. Common to these devices is a straight-line magnetostrictive wire, an actuator for inducing a torsional strain at a given position along the wire (generally a piezo electric crystal), and a magnet, which is displaceable along the wire. The induced torsional strain propagates down the wire and is detected by a magnet, which represents the position of the monitored quantity. The time differential between excitation and detection of the torsional signal determines the distance between the actuator and the magnet, thereby allowing computation of the distance between the actuator and magnet.
A common problem encountered by prior art devices is finding suitable equipment to mechanically link the actuator (generally, a piezoelectric crystal) to the magnetostrictive wire. Some prior art devices welded the wire to the actuator, creating a connection that is easily broken. Koski eliminates the welded contact by providing a removable clamp to hold the MS wire against the piezo crystal, using elastomeric pads between the crystal and clamp. The removable clamp allows one to adjust the compressional force between the piezo crystal and magnetostrictive wire. The Koski structure helps solve the problem with breakage of the connection, but in practice, it is awkward and time inefficient to assemble and can result in inefficient coupling (too little clamping force) or breakage of the piezo crystal (too much clamping force).
The present invention provides a one-piece actuator housing for the piezo actuator. The housing contains a slot through which the magnetostrictive wire passes. The piezo actuator is also placed in the slot in contact with the magnetostrictive wire. An elastomeric cushion is placed around the wire/actuator, the cushion sized to fill the space in the slot. The housing also has a tail end designed to reside in the outer sleeve of the magnetostrictive device.
It is an object of the invention to provide a one-piece actuator housing.
It is an object of the invention to provide a structure for providing good mechanical contact between the piezo crystal and the magnetostrictive wire without the need of a clamp.
It is an object of the invention to provide a structure for providing good mechanical contact between the piezo crystal where the contact pressure is not variable or adjustable.
It is an object of the invention to provide a structure for providing good mechanical contact between the piezo crystal where a predetermined contact pressure can be readily established.
It is an object of the invention to provide a one-piece actuator housing of dimensionally stable components to allow the frictionally inserted components to be installed with predictable mechanical results.
It is an object of the invention to provide an actuator housing which can be inserted into one sleeve of the magnetostrictive housing and allowing that housing to be threadably attached to another sleeve.